1. Field of the Invention
The present invention relates to a television receiver, and more particularly, to a tuner unit having a UHF section and a VHF section controlled by a phase-locked loop section, for example.
2. Description of the Related Art
A prior art tuner unit includes an antenna input filter section, a UHF section and a VHF section both of which are connected to the antenna input filter section, and a control section such as a phase-locked loop (PLL) section. The UHF section includes a high frequency amplifier as a preamplifier stage, a local oscillator, and a mixer for mixing an output of the high frequency amplifier with an output of the local oscillator, to thereby generate an intermediate frequency (IF) signal. Similarly, the VHF section includes a high frequency amplifier as a preamplifier stage, a local oscillator, and a mixer for mixing an output of the high frequency amplifier with an output of the local oscillator, to thereby generate an IF signal. The frequencies of the two local oscillators are controlled by the PLL section.
The antenna input filter section, the UHF section, the VHF section and the PLL section are conventionally mounted on a single printed circuit board, and each of the sections is electromagnetically separated from each other by electromagnetic shields (hereinafter referred to as "walls"). This will be explained in detail later.
In the prior art tuner unit, however, an inductor for the VHF local oscillator is easily vibrated to fluctuate the frequency of the VHF local oscillator, thus generating noise in a television reception image. Also, in the VHF section, since the inductor for the VHF local oscillator and a load inductor for the mixer are located in the same section, the output signal of the VHF local oscillator is leaked to a post stage such as an IF amplifier and to the exterior. Further, particularly in the UHF section, since the distance between the local oscillator and the mixer is large enough to increase the stray capacity of the local oscillator, the operation of the local oscillator in a high frequency region is unstable at a high temperature. Still further, each of the oscillators is located in proximity to an integrated circuit of the PLL section so as to reduce the interference of spurious signals generated from the oscillators, thus improving the characteristic of the tuner unit. In this case, however, the integrated circuit for the PLL section is so distant from a data input portion for the PLL section that digital signals applied to the data input portion affect the operation of the tuner unit and the IF amplifier.